Contact microphones adapted to engage the throat or other vibrating body portion adjacent to the larynx of a wearer are well known in the art. Such microphones are particularly advantageous in noisy environments since they rely on direct mechanical coupling to the larynx of the wearer rather than merely acoustic coupling as in the usual arrangement. On the other hand, the nature of the mechanical coupling produces a severe attenuation at high frequencies, particularly those frequencies above about 350 hertz containing most of the intelligible information.
Various attempts have been made in the prior art to improve the high-frequency response of throat microphones. For example Kuhlik U.S. Pat. No. 2,385,867 discloses an arrangement in which a dynamic microphone is placed inside a sound box that is adjacent to the larynx of the wearer. According to the patentee, the sound box acts as a resonance chamber emphasizing voice frequencies. Although the sound box is said to eliminate noise, the construction is such that it responds to all mechanical vibrations, not merely those emanating from the throat.
Other contact microphones, such as those shown in Greibach U.S. Pat. No. 2,255,249, Sears et al U.S. Pat. No. 2,260,727 and Stanley U.S. Pat. No. 2,340,777, use resonating mechanical elements inside the microphone housing to provide the desired emphasis in the voice range. In one embodiment shown in the Sears et al patent, the mechanical resonator also includes a button adapted to engage the flesh of the wearer. In each of the devices disclosed, the mechanical resonators are directly coupled mechanically to the resistive or electromagnetic transducer element of the microphone. Such resonators would be relatively unsuitable for use in conjunction with electret microphone elements, the diaphragms of which are very light and cannot be loaded mechanically without drastically altering their performance.
Still others have sought to obtain a desired rising response characteristic from a throat microphone purely by electrical means. Thus, Ballantine U.S. Pat. No. 2,121,778 discloses various filtering networks including one in which a grid leak resistor forms a differentiator with a piezoelectric microphone crystal. Although electrical filters of the type disclosed in this patent are useful in shaping the response of a throat microphone, they must be used in stages to obtain a sharply rising or falling response characteristic.